264 SIX NEW SPECIES 



naturalist is therefore obliged to abandon this character as al- 

 most useless. In noticing the colouring of the epidermis we 

 must not pass unobserved the peculiar spots which are found 

 on the cylindricus of Say, the metanevra of Rafinesque, and 

 triangularis of BarneS. These have generally the form of 

 an arrow-head, but sometimes so much elongated as to form 

 rays. The hair like rays of the cornutus of Barnes and its 

 varieties are peculiarly beautiful in fresh and perfect speci- 

 mens ; and the spotted lines covering the irroratus over its 

 whole disk will yield to none of the painted epidermides. 



In the measurements I have adopted the plan of Barnes : 

 the greatest transverse line is the breadth, the greatest line 

 perpendicular to this is the length, and the greatest line per- 

 pendicular to those lines, that is, from the most ventricose 

 part of one valve to the most ventricose part of the other, is 

 the diameter. We thus have the three greatest measure- 

 ments of the shell, and the marginal descriptions give the 

 form. It should be remembered that different localities pro- 

 duce various sizes, and even the thickness of the shell is 

 frequently changed from this circumstance. 



In considering the word "Unio" as of the masculine gen- 

 der, I have followed the American conchologists, in oppo- 

 sition to Lamarck and other Europeans, who consider it as 

 feminine. Ainsworth, in that part of his dictionary ap- 

 propriated to pure Latinity, gives the following definition : — 



Unio, onis, m. (ab unus, quod in conchis nulli duo reperi- 

 antur indiscreti, i. e. similes,) .5 pearl, called a union, because, 

 many being found in one shell, not any of them is like the 

 other. Plin. 9, 35. Unionum conchas, mother of pearl. Suet. 

 Ner. 31. 



In Ainsworth 's " Index Vocum Vitandarum" is to be found 

 the following definition : — 



Unio, onis, /. (quod unum facit) Union, concord, agree- 

 ment; the number of one, Theol. {In this latter sense it 

 must be masculine, as ternio, senio, &c. *J. C.) 



* J. C. John Carey, the editor of the last edition of Ainsworth's quarto dic- 

 tionary. 



